This review describes the current state of research on the formation of a nanocrystalline structure in amorphous alloys under thermal and deformation effects. The processes of formation of nanocrystals in homogeneous and heterogeneous amorphous structures (nanoglass) are considered. Changes in the magnetic and mechanical properties during the formation of a composite amorphous-nanocrystalline structure with different structural parameters are analyzed. The possibility of amorphous phase rejuvenation from a partially crystalline structure under cryogenic thermocycling treatment is shown.

Abstract The structure of deformed Al-based amorphous alloys was studied by X-ray diffraction, scanning, transmission and probe electron microscopy. It has been found that the material in the shear bands has lower values of Young’s modulus and density. The shear band width is about 50 nm. In the band, no redistribution of the alloy components typical for phase separation is observed. The size of the regions with reduced Young’s modulus around the shear band is in the range from several tenths of a micron to 1 µm.

Abstract Studies of the structural evolution of the group of Al-based amorphous alloys of Al-Ni-RE (RE = La, Y, Gd) systems showed that, under the combined action of heat and deformation on the structure, one may obtain samples with different crystal sizes and different fractions of the nanocrystalline phase. Under crystallization of a heterogeneous amorphous phase, the size of the nanocrystals is smaller, and their fraction is larger than under crystallization of a homogeneous amorphous phase. The use of cryogenic cycling method allows rejuvenating the amorphous phase in partially crystalline alloys.

Crystallization process of Al90Y10 amorphous alloy after heat treatment is investigated. Analysis of the structural transformations after heat treatment makes it possible to estimate the activation energy of crystallization and the diffusion coefficient in the deformed amorphous phase. Kissinger and Augis-Bennett models are employed to obtain the activation energy of the as-quenched alloy based on the differential scanning calorimetry (DSC) data. The crystallization of Al90Y10 amorphous alloy at high pressure torsion (HPT) is studied and the kinetic characteristics of crystal growth in a deformed matrix are determined. It is established that the nanocrystalline Al phase precipitates in the alloy subjected to HPT. The size of Al nanocrystals is measured to be about 9 nm and does not depend on deformation degree. It is suggested that the nanocrystallization of amorphous alloy during deformation is due to the simultaneous effect of structural changes in the amorphous matrix and of a local increase of the temperature during HPT processing. The local temperature increase at the crystallization front is estimated to be about 120 K.

Sulfide melt inclusions entrapped in primitive olivine phenocrysts can be used to understand the compositions of early sulfide melts that may ultimately contribute to magmatic sulfide ore deposits. Sulfide globules hosted in olivine (86–92mol% Fo) from the Tolbachik basalt (the 1941 eruption) are characterized in terms of their major and trace element abundances using electron microscopy and LA–ICP–MS analysis. Distribution of major elements within individual sulfide globules varies from homogeneous to heterogeneous. Phases include monosulfide solid solution (MSS) and intermediate solid solution (ISS) intergrowths and exsolved low-temperature minerals such as pyrrhotite, pentlandite, chalcopyrite and cubanite. Trace elements (platinum-group elements — PGE, Ag, Te, Au, Pb and Bi) are also present in solid solution in sulfide phases and as micron-sized particles (“nuggets”). Such nuggets of dominantly Au, Pt, Au–Pd and Pd–Te are contained randomly within sulfide matrices or, more commonly, at phase boundaries. Nuggets are also attached to outer surfaces of sulfide globules. Concentrations of PGE in sulfides follow a log normal distribution over four orders of magnitude. The highest measured noble metal concentrations in the analyzed globules (436ppm Au+PGE) are 13.3ppm Au, 115ppm Pt and 299ppm Pd, whereas 40% of globules have <15ppm of noble metals. Gold and PGE concentrations correlate, suggesting these elements were concentrated by the same process(es). We propose that a number of anomalous concentrations of one or several noble metals in the analyzed globules can be best explained by entrapment of Au–PGE-rich particles (solid or liquid) from the silicate melt. Although the individual Tolbachik sulfide globules have variable PGE abundances, their mean composition resembles those of major PGE-sulfide ore deposits (e.g., Norilsk, Sudbury, Platreef and Merensky Reef).

The influence of heat treatment and deformation on structural changes of Al-based amorphous alloys in the amorphous state and at early stages of crystallization has been studied using the methods of X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. It is shown that isothermal annealing and multiple cold rolling bring about formation of an inhomogeneous amorphous phase with the areas of different chemical composition. The formation of an inhomogeneous amorphous phase accelerates the process of nanocrystallization of Al-based alloys. The conditions of treatment of the amorphous alloy in the amorphous state affect the size and fraction of nanocrystals forming in the amorphous phase upon subsequent heating. The size of nanocrystals in the case of preliminary deformation is smaller than that upon preliminary isothermal annealing. We discuss the reasons for the formation of nanostructures containing smaller nanocrystals in the case of thermal and deformation treatments before the onset of crystallization.

Structure evolution of amorphous alloys at heat treatment and deformation is discussed. Amorphous structure change before crystallization is considered for Al-, Ni-, Fe-, Zr-based systems. Property change with structure evolution is discussed as well. Nanocrystal formation in light metallic glasses is studied at heating and deformation. The sizes of the nanocrystals forming during plastic deformation were found to be smaller than those of the nanocrystals forming on thermal treatment. The sizes of the nanocrystals do not change (Al-Ni-Gd, Al-Y) or change only slightly (Al-Ni-La) with increasing degree of plastic deformation whilst their volume content increases and the fraction of nanocrystals in the deformed samples is larger than that in the samples subjected to thermal treatment. Using combined treatment (plastic deformation + annealing) was observed to result in intermediate nanocrystals size.

Formation of aluminum nanocrystals in light Al90Y10 and Al87Ni8Gd5 amorphous alloys at heating and deformation was studied by X-ray diffraction and electron microscopy methods. High pressure torsion and multiply rolling were used for the deformation influences. The average size of the nanocrystals induced by deformation was found to be lower than that formed during the heat treatment. Combined treatment (deformation+annealing) leads to the formation of nanocrystals of intermediate size. Increasing the deformation degree leads to an increase in the fraction of the nanocrystalline phase. The dependence of the microhardness of amorphous - nanocrystalline structure on the deformation degree was measured. Increasing the deformation degree (and thus rising fraction of the nanocrystalline phase) increases the microhardness of the alloys. The value of the microhardness, close to a record for light Al-based alloys is obtained for amorphous-nanocrystalline Al87Ni8Gd5 alloy.

The effect of high stress and high temperature on the structure of binary Al90Y10 amorphous alloy has been investigated. Deformation of the alloy was carried out by high pressure torsion at room temperature; heating was produced up to 220 degrees C.It was revealed that both treatments leaded to the primary crystallization of the alloy. Produced Al nanocrystals were randomly distributed over the amorphous matrix. For the deformed sample no correlation between the location of nanocrystals and the positions of shear bands was observed. The nanocrystals formed due to the deformation were more euhedral and smaller in average size (similar to 9 nm) than those produced by heating (similar to 15 nm). We have shown that the size distributions for two states of the alloy differ from each other substantially. Based on the obtained data for Al nanocrystals size distribution we have concluded that the deformation-induced nanocrystallization in Al90Y10 occurs by heterogeneous mechanism and the crystallization at the heating takes place by the mixed (heterogeneous and homogeneous) one. (C) 2014 Published by Elsevier B.V.

Nanocrystallization of Fe78Si13B9 metallic glass under severe plastic deformation was studied by X-ray diffraction and electron microscopy methods and by magnetic property measurements. The plastic deformation of the alloy was carried out by high pressure torsion at a pressure of 4GPa at room temperature. Deformation was performed by unidirectional torsion and involves serial to-and-fro torsion. Severe plastic deformation of amorphous Fe78Si13B9 alloy was found to induce nanocrystallization with formation of Fe (Si) nanocrystals. The average size of the nanocrystals is 6nm and a volume fraction of the nanocrystalline phase is more than 50% of the sample. The formation of the nanocrystalline structure leads to increase in saturation magnetization by 40% without appreciable changes of the coercivity.

The effect of multiple rolling at room temperature on the structure and crystallization of the Al85Ni6.1Co2Gd6Si0.9 amorphous alloy has been studied using transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction. The total plastic strain is 33%. It has been shown that the deformation results in the formation of aluminum nanocrystals with the average size that does not exceed 10–15 nm. The nanocrystals are formed in regions of localization of plastic deformation. The deformation decreases the thermal effect of nanocrystallization (∼15%) as compared to the heat release at the first stage of crystallization of the unstrained sample. The morphology, structure, and distribution of precipitates have been investigated. Possible mechanisms of the formation of nanocrystals during the deformation have been discussed.

Formation of nanocrystalline structure in amorphous Fe-B-Si alloy under severe plastic deformation was studied by X-ray diffraction and transmission electron microscopy. Severe plastic deformation of the alloy has been carried out by high pressure torsion method with a pressure of 4 GPa. The severe plastic deformation was found to lead to an appearance of Fe(Si) nanocrystals in the amorphous matrix. The nanocrystal size is independent of the deformation level and they formed by diffusion mechanism of crystallization. When the deformation degree increases, the volume fraction of the nanocrystalline phase also increases. The average size of the nanocrystals formed at severe plastic deformation was found to depend on the deformation temperature. The nanocrystalline phase formation may lead to increase saturation magnetization.

Model SOFCs with Sr0.7Ce0.3MnO3 cathode were found to display nonlinear current-voltage characteristics resulting from changes in the interface resistance with varying current load. Short-term tests (~200 hours) of the cell performance were carried out at a current load of 81.5 mA/cm2. The resource tests demonstrated high stability of power performance of the model SOFCs. The Sr0.7Ce0.3MnO3 material was concluded to be a promising cathode for intermediate-temperature SOFCs.

The structure and mechanical properties of bulk Zr50Ti16.5Cu15Ni18.5 metallic glasses were studied by X-ray diffraction, scanning and transmission electron microscopy and by measurements of mechanical properties. The transition from heterogeneous to homogeneous deformation was found to occur at 575 K. The crystallization was found to begin in the testing part of the sample earlier than in the part placed in a holder during the mechanical testing. The crystallization leads to the formation of the quasicrystalline phase with a0 = 2.54 Å, hexagonal phase ZrTi(Ni,Cu) and hexagonal phase (Zr6CoAl2 type). The difference of the structure in different parts of the sample has been observed and analyzed. The deformation does not effect on the crystallization processes occurring during the tensile testing at this temperature and the crystallization proceeds owing to the self-heating of the samples during the phase transition. The correlation between mechanical properties, structure and fracture surfaces is discussed.